In a CL composed of a hard portion in the central part and a soft portion in the periphery thereof, the edge part is composed of a soft portion, which reduces feeling of foreign objects during the use thereof, thus, some of such CL have been produced (JP-A-49-87345, JP-A-56-50313 and JP-A-50-25245).
JP-A-49-87345 discloses a preparation process of a CL comprising a hard transparent body in the central part and a soft transparent polymer in the peripheral part thereof, which is produced from a plate material obtained by forming a cylindrical laminate having a soft transparent polymer layer around the cylindrical hard transparent body closely bonded therewith by polymerizing a monomer providing a soft transparent polymer that is softened and swelled by water around the cylindrical hard transparent body, and thinly cutting the laminate in the cross sectional direction.
JP-A-56-50313 discloses a CL comprising a central part of the lens having a larger hardness than a peripheral skirt part and a polymer matrix capable of compounding with a material forming the central part of a lens with hydrophilic property and water swellability.
However, in the CL described in these references, oxygen permeability of the obtained CL is low, since a silicone-containing monomer is not contained in a monomer mixture forming a hard portion, and when the CL is continuously used, a possibility of a deficiency in oxygen supply to corneas is high. Further, a previously prepared hard portion is arranged in the center, and a monomer mixture forming a soft portion is polymerized in the periphery thereof. In this case, the hard portion and the soft portion are not favorably connected, and there has been a problem of inferiority in terms of strength. In addition, centering of the hard portion requires complicated procedures.
JP-A-50-25245 discloses a preparation process of a CL comprising a hard material in the central part and a soft material in the periphery of the central part, which is prepared from a laminate arranging a transparent material (a hard material) that is not softened by water inside of a cylindrical or plate material having a void and comprising a transparent material (a soft material) that is softened by water. However, a silicone-containing monomer is not contained in a monomer mixture forming the hard material, thus, oxygen permeability of the obtained CL is low, and when the CL is continuously used, there is a possibility of a deficiency in oxygen supply to corneas, and since a hydrophilic monomer is not also contained, connection with the soft material is not favorably carried out, and there is a problem in inferiority in terms of strength.
An object of the present invention is to provide a CL excellent in optical property, offering favorable feeling during the use thereof, and capable of continuous use, which is composed of a hard portion in the central part and a soft portion in the periphery of the central part.